Effect of Bicarbonate Ion on the Respiration of Excised Roots

Investigations have established the bicarbonate ion as a contributing factor in a plant chlorosis similar to that induced by soils high in calcium carbonate. This type of plant yellowing associated with an inactivation of iron is referred to as chlorosis in this paper. Chlorosis has been induced in susceptible plants by increasing the level of the bicarbonate ion in the growth medium (5, 8). A combination of high pH and high bicarbonate ion concentration has not prevented iron absorption, but apparently has resulted in the inactivation of iron within the plants. Lindsay and Thorne (5) found that nutrient solutions containing high bicarbonate ion concentrations increased the accumulation of iron in the roots of Great Northern bean plants, but decreased the translocation to leaves and stems. Similar results were obtained by Warnock (11). The bicarbonate ion effect cannot be attributed to high pH alone. Porter and Thorne (6) conducted nutrient culture experiments in which pH and bicarbonate ion concentrations were varied by regulating the carbon dioxide pressure of the aeration stream. Great Northern bean plants developed chlorosis with high bicarbonate ion concentrations regardless of pH. Stewart and Preston (7) found that the bicarbonate ion, more than anv other component of a bicarbonate buffer solution, suppressed the uptake of bromide ions bv potato disks. Increasing the level of KHCO3 in the solution depressed protein synthesis and oxidase activity. Plants differ in susceptibility to chlorosis (1, 5, 11). Brown (1) investigated some copper and iron enzymes in a group of plants in relation to chlorosis susceptibility. Plants of the group which become chlorotic when grown on a high-lime soil were resistant to chlorosis when grown on an organic (copper deficient) soil. Plants which were chlorotic when grown on a calcareous soil were much lower in catalase activity than were green plants of other species grown on the same soil or of green plants of the same species grown on different soils. Ascorbic acid oxidase appeared to be a good index of available copper in most plants whether the plants did or did not show visual copper deficiency symptoms. Since the known functions of copper and iron in plants are associated solely with enzyme systems, the difference in behavior of chlorosis-susceptible and chlorosis-resistant plants indicates differences in the relative dependence of these plants on iron and copper enzyme systems. Kadry (4) has noted a pronounced accumulation of bicarbonate-derived carbon in several plants. The pronounced effects of the bi-